websocket: Enforce Sec-WebSocket-Protocol header to be in ASCII
websocket: Enforce Sec-WebSocket-Protocol header to be in ASCII

The value of this header is being split into words. This *might* lead to
weird results if the value contains multi-byte characters. As valid
values can only contain ASCII anyway, let's enforce it to be on the safe
side.

martinpitt/cockpit,martinpitt/cockpit,deryni/cockpit,moraleslazaro/cockpit,deryni/cockpit,cockpituous/cockpit,cockpituous/cockpit,garrett/cockpit,cockpituous/cockpit,deryni/cockpit,moraleslazaro/cockpit,deryni/cockpit,cockpituous/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,cockpituous/cockpit,garrett/cockpit,cockpit-project/cockpit,deryni/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,garrett/cockpit,moraleslazaro/cockpit,garrett/cockpit,cockpit-project/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,deryni/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,garrett/cockpit,martinpitt/cockpit,cockpit-project/cockpit,deryni/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,cockpituous/cockpit